The invention is based on a leveling system for vehicles.
In a known leveling system of this type (German Patent Disclosure Document 39 10 030 A1), two restoring springs acting contrary to one another are provided for the control slide; in its uncontrolled state, they keep it in a middle position of its displacement travel, in which all the valve connections are blocked. With its axial end faces, the control slide, on one side, defines the control chamber that communicates with the pilot control valve and is connected via a throttle to the valve connection for the pressure fluid source, and on its other side it defines a pressure chamber, which communicates via a further throttle with the valve connection for the work cylinder or actuator, so that the pressure of the actuator is fed back to the control slide. The valve outlet of the pilot control valve communicates via a throttle with the valve connection for the pressure fluid tank of the main valve. A closing valve is disposed in the return line from the aforementioned valve connection to the pressure fluid tank; it is connected by its control inlet to the connecting line from the pressure fluid source to the main valve. The closing valve is designed such that it is opened as long as the control pressure in the connecting line is greater than a specified value. If the control pressure drops below this value, the closing valve closes. The pressure in the return line upstream of the closing valve rises and then adjusts to the pressure prevailing in the work cylinder. As a result, no pressure fluid pressure in the actuator is bled off. The actuator maintains its pressure, unchanged.
When the vehicle having the known leveling system is started up, pressure surges can occur in the work cylinder as the leveling system begins to operate, and a resultant sudden shift in the vehicle body can endanger passengers.